1. Field of the Invention
This invention relates to pumps and more particularly to a combination paint and air pump.
2. Prior Art
Modern paint spraying equipment can be generally divided into two categories, air and airless. In air paint spraying, an air pump is used to provide a source of pressurized air which is intermixed with the paint by various means, including aspiration, to provide an atomized paint and air spray. In airless painting, the pump operates directly on the paint to force it at high pressure through a nozzle orifice where the paint is atomized providing a paint only spray.
Recently, it has been found desirable in many instances to surround the cone or fan of the spray pattern with an air or other gas stream. This type of spraying includes numerous variations, including some where an airstream is directed at the paint stream, particularly in association with airless paint spraying, and others where an airstream is formed as a shield radially exterior of the paint stream. In some forms of liquid spraying, it has been known to use an inert gas for the shield, however in most present embodiments, the shield or admixed gas is air. The obtaining of a separate air supply is relatively uncomplex when air spray painting is used since the air compressor can be used to supply both air for creation of the paint stream and air for creation of the secondary gas stream. However, in airless spray painting, no such gas supply is presently available and therefore such systems require the provision of separate air sources such as, for example, separate air compressors or factory line compressed air. It would therefore be an advantage to provide a single device which is capable of supplying both liquid at high pressure for airless spraying and pressurized air for the separate airstream.
Presently used airless paint spray equipment is most prominently of the diaphragm pump type where a prime mover reciprocates a piston to load and unload an hydraulic column in a driving fluid chamber. The driving fluid chamber is separated from the paint or driven fluid chamber by means of a diaphragm. Loading and unloading of the hydraulic column causes reciprocation of the diaphragm. Through appropriate valving, liquid to be sprayed is first drawn into and then expelled under pressure from the driven fluid chamber. Devices of this type are shown in U.S. Pat. Nos. 3,254,845 and 3,367,270 to Schlosser.
The drive to the piston may take many forms from use of an oscillating crank to the use of a wobble plate as shown in U.S. Pat. No. Re. 29,055 to Wagner, to the use of an eccentric cam wheel drive such as shown in U.S. Pat. Nos. 3,430,557 and 3,623,661 to Wagner, or other oscillating type connections. Common to all drive connections is the imparting of a reciprocating movement to the hydraulic column drive piston. Normally the drive connection is contained within a housing which forms an oil reservoir for the driving fluid with the cylinder in which the piston reciprocates being provided in a bore through an outside wall of the housing. Such a construction is shown in my prior U.S. Pat. No. 4,022,381 which utilizes an eccentric cam wheel drive.
When such prior art airless paint spray equipment is presently used with a painting system requiring the use of an additional gas source, such as for air surround painting, it is necessary to provide a separate compressed air supply. Since such prior airless paint spray equipment has a distinct advantage of ease of mobility, airless paint spraying has found wide-spread use in locations where compressed air is not readily obtained. Thus, to use spraying techniques calling for both airless spray painting and air supply, it has heretofor been necessary to bring to the painting site additional equipment for supplying the compressed air. This can lead to difficulties where the high pressure paint is utilized at a remote spray gun which also utilizes the air. In such situations two separate pressure lines must be provided to the remote gun. To the extent that these two pressure lines originate at different mechanisms, i.e. the paint pump and the air compressor, line entanglement, difficulty in ease of repositioning of the equipment and other disadvantages will occur. It would therefore be an advance in the art to provide a single pumping device which provides separate pressurized liquid and gas streams from a common drive. It would be a further advance in the art if such equipment could be used either for the simultaneous supply of liquid and gas or for the individual supply of liquid or gas.